Yeah, I suppose you're right. Ultimately in such a tracing effort I imagine they probably would encounter a bunch of telcos passing the buck until it gets to a dissolved overseas entity who cannot be held responsible for anything.
I'll keep repeating this one forever, but - that's not an issue. This would end spam calls immediately: "if you can't tell who's the source or if the source is international, you're responsible and will be fined per spam call".
Telcos are not clueless or powerless. They can put pressure on international peers to not send spam, but have no incentive currently. No real telco wants to lose partners.
